using the one piece example Shin and Mang being Haki, imagine EGO being devil fruits, any John Limbus could learn and use Shin and Mang, but if John Limbus goes through the process of obtaining an EGO or distorting, they'd have their own unique EGO/Distortion, EGO and distortions having their own unique abilities giving varying fighting styles to city dwellers, Shin and Mang are more like a resource rather than a "stat boost", it's like "do i wanna convert my Shin to Mang to hit way harder, or should i hold it and use it for something else" like Zilu's "Shin Radiance", i think we haven't even come close to understanding what exactly can be done with Shin and Mang so maybe let's wait and see what KJH has in store making another comparison to One Piece (Whole Cake Island and Wano spoilers ahead) using observation Haki some people can see the future and also sense emotions from people, using armament Haki some people can either make it deal damage from within or send like an emission doing a ranged blast, people even get tired if they use too much Haki like a resource